This answer is overly simplistic, but I would place the ANV's major obstacle to success in the Overland Campaign to be General US Grant himself. Grant was relentless, but early in the campaign his hell-bent-for-leather determination to succeed at all and any cost may have been underestimated and under appreciated by many in the ANV high command.

Another factor mitigating against the ANV was that if one could call the Civil War a war of attrition, the weight of attrition was beginning to be felt by the South especially in terms of manpower.

That said, Grant's army may have also underestimated the determination of Lee's army at least initially. So we had two very worthy foes willing and able to fight to the last man in order to end the conflict once and for all. That fact alone presented each side with considerable and costly obstacles to the success of the other.

This answer is, of course, an oversimplified answer to a campaign that faced complex issues as all major campaigns in the CW did.

The US had bad maps, a continuous supply problem, lousy roads, too many wheeled vehicles and a constricted area for maneuver. The Confederates suffered from the middle 2 as well.

The US supply line depended on extending a line of depots down the Potomac. In effect, a new depot was alwasy being built ahead of the last one, requiring double the effort and manpower. Wagons frequently showed up at the 'wrong' depot only to find it was being decommisioned in order to leapfrog ahead.

Lee's supplies came up, and wounded went down, the RF&P, a flimsy single track line much the worse for wear from already serving military needs for 3 years.

Grant reduced both the number of cannon and the number of supply wagons accompanying the troops. The QM also devined a better way of moving supplies from the main depot to a series of ever smaller depots down to the brigade level where fewer wagons were used on the last leg to the troops. However it required more reloading of the supplies from wagon to wagon.

Poor maps and bad roads were the bane of virtually every campaign.

In Grant's moves to the left, the basic procedure was to dig in, have the right-most corps decamp, march behind the other 2 corps and take up the far-left position. Like a track on a bulldozer, each corps would be in front for a bit, stay in place for a while, become the rear guard and then move a long way to repeat the process.